Old-growth Acer macrophyllum trees host a unique suite of arbuscular mycorrhizal fungi and other root-associated fungal taxa in their canopy soil environment

ABSTRACT

Canopy soils occur on tree branches throughout the temperate rainforests of the Pacific Northwest Coast and are recognized as a defining characteristic of these ecosystems. Certain tree species extend adventitious roots into these canopy soil environments. Yet, research on adventitious root-associated fungi remains limited. Our study used microscopy to compare fungal colonization intensity between canopy and forest floor roots of old-growth bigleaf maple (Acer macrophyllum) trees. Subsequently, two high-throughput sequencing platforms were used to explore the spatial and seasonal variation of root-associated fungi between the two soil environments over one year. We found that canopy and forest floor roots had similar colonization intensity and were associating with a diversity of arbuscular mycorrhizal fungi and other potential symbionts, many of which were resolved to species level. Soil environment and seasonality affected root-associated fungal community composition, and several fungal species were indicative of the canopy soil environment. In Washington State’s (USA) temperate old-growth rainforests, these canopy soil environments host a unique suite of root-associated fungi. The presence of arbuscular mycorrhizae provides further evidence that adventitious roots form fungal associations to exploit canopy soils for resources, and there may be novel relationships forming with other fungi. These soils may be providing a redundancy compartment (i.e., “nutrient reserve”), imparting a resiliency to disturbances for certain old-growth trees.

KEYWORDS:

• Adventitious roots
• canopy soils
• dark septate endophytes
• fungal communities
• mycorrhiza
• root-associated fungi
• temperate rainforests

Acknowledgments

We thank the Olympic National Park (study no. OLYM-00034) and The Nature Conservancy for granting research permits. We also thank the School of Environmental and Forest Sciences Genetics Laboratory, Tom Deluca, and also the late Benjamin Hall for providing access to laboratory space. We are grateful for Zue Leika, Anne Polyakov, Lizzy Stone, Michael McNorvell, Jalene Weatherholt, Scott Mafune, Beverly Mafune, and Jason LaBay for assisting with field sampling. We also thank Joe Ammirati for feedback throughout the duration of this project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

DATA AVAILABILITY

The raw sequence files for both the MinION and Illumina MiSeq sequence runs have been deposited in the National Center of Biotechnology Information’s (NCBI) database and are available in the Sequence Read Archive (SRA) under the BioProject ID no. PRJNA833545. MinION BLAST IDs and barcode metadata have been deposited in Zenodo and are available through the associated DOI 10.5281/zenodo.7478672. The python scripts used for the MinION are available at https://github.com/mycoophile/nanopore-ITS.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00275514.2023.2206930

Additional information

Funding

This study was funded by grants from the Mycological Society of America, the Daniel E. Stuntz Memorial Foundation, the University of Washington’s Ben Hall Conservation Genetic fund, Oregon Mycological Society, Puget Sound Mycological Society, and Sonoma County Mycological Society; Daniel E Stuntz Memorial Foundation.